Soybean Background

• Soybean is an essential crop in the United States
• Used for food and oil
  • Primarily for feeding livestock and producing cooking oil

A new pest

• In 2011, there were reports of an unidentified orange larvae on the stems of damaged soybeans after a hailstorm
• Entomologists received reports of larvae infestations in 2018 for an unknown species causing significant damage

A new pest

• Initial surveys indicated the infestation was in Minnesota, Iowa, South Dakota, and Nebraska
• As of 2020, the insect was identified in 114 counties, now including Missouri

A new pest

• Initially found on damaged plants at the end of the growing season, causing little economic concern
• In 2018, an infestation warranted further concerns when a sample of damaged plants from earlier in the growing season had no other detectable plant diseases
• Insects were identified as a new species in the Resseliella genus
• Females lay eggs in damaged parts of soybean stems (including naturally occurring fissures) and larvae eat away at the stem

Possible solutions

• At this time, there are no guaranteed methods for preventing damage due to soybean gall midge

• One possible method, the subject of today’s talk, is to cover the stems of soybeans with dirt

  • A process known as hilling

Hilling Study

Does hilling at a particular stage in the soybean growth cycle help to decrease the number of soybean gall midge (SGM) larvae?

• In 2022, a study was conducted as a randomized complete block design (RCBD) and measured the count of SGM larvae.
  • An infested field had four rows where each row was used as a block
  • Within each field row, four treatments were randomly applied to a section
    • No hilling (control)
    • Hilling at V2, V5, and R2 soybean growth stages
  • Measurements were taken at approximately two-week intervals

Hilling Study: Fitted Model

Where

• \(\eta\) is the intercept

• \(\tau_i\) is the \(i^{th}\) hilling date

• \(S_j\) is the \(j^{th}\) sample date

• \((\tau S)_{ij}\) is the interaction between the \(i^{th}\) hilling date and the \(j^{th}\) sample date

• \((B \tau)_{ik}\sim N(0, \sigma^2_{A})\) is the random interaction effect between the \(i^{th}\) treatment and the \(k^{th}\) field row

• \(S(B\tau)_{ijk}\sim N(0, \sigma^2_{B})\) is the random effect of the \(i^{th}\) hilling date, \(j^{th}\) sample date, and the \(k^{th}\) row

• Distribution: \(y_{ijk}|(B \tau)_{ij}, S(B\tau)_{ijk}\sim Poisson(\lambda_{ijk})\), where \(y_{ijk}\) is the count of SGM larvae

• Link function: \(\eta_{ijk}=\log(\lambda_{ijk})\)

Hilling Study: Results

• Some evidence of interaction between sample date and timing for application of hilling
• Only a few differences detected
  • July 5, differences between control and V2 (Treatments 1 and 2, p-value = .0203) and between V2 and R2 (Treatments 2 and 4, p-value = .0351)
• Possible evidence that hilling at the V2 stage help reduce SGM larvae counts?

Unhilling Study

Two primary research questions:

1. How does unhilling affect total SGM larvae counts? / Does having a preventative measure earlier in the growing season decrease SGM larvae counts?

2. How does unhilling affect soybean growth/yield?

• Study design is similar to the hilling study (RCBD)

  • Field organized into two rows and two columns, with each section acting as a block

  • Seven treatments of unhilling dates approximately two weeks apart (one left unhilled at the start of the study as a control)

  • For (1), larvae counts were taken approximately every two weeks

  • For (2), growth/yield metrics were taken at the end of the growing season

Unhilling Study: Fitted Model (1)

• Terms are defined the same as the hilling study
• \(y_{ijk}| S(B\tau)_{ijk}\sim Poisson(\lambda_{ijk})\)
• \(\eta_{ijk}=\log(\lambda_{ijk})\)

Unhilling Study: Results (1)

Differences marked with an asterisk (*) are considered marginally significant. There were no other significant simple effect differences for each sample date.

Unhilling Study: Results (1)

Larger treatment numbers denote a later date for unhilling. Trends indicate that unhilling earlier in the season have larger counts of SGM larvae.

Unhilling Study: Fitted Model (2)

The full model is presented for the five collected responses. These are count of soybean nodes, pods, seeds, and plant height and seed weight.

Where

• \(\eta\) is the intercept

• \(B_i\sim N(0, \sigma^2_B)\) is the effect of the \(i^{th}\) field section (block)

• \(\tau_j\) is the effect of the \(j^{th}\) unhilling date

• \((B\tau)_{ij}\sim N(0, \sigma^2_{B\tau})\) is the interaction effect of the \(i^{th}\) field section and the \(j^{th}\) unhilling date

• \(\epsilon_{ijk}\sim N(0, \sigma^2_e)\) is the random error of the \(i^{th}\) field section, \(j^{th}\) unhilling date, and the \(k^{th}\) plant

The model is then fit the these specifications

Unhilling Study: Results (2) - Soybean Height

In general, unhilling earlier in the growing season decreases soybean height

Unhilling Study: Results (2) - Soybean Height

Unhilling Study: Results (2) - Soybean Seed Count

Unhilling Study: Results (2) - Soybean Seed Count

Similar to soybean height, unhilling earlier in the season generally decreased soybean seed counts

Discussion

STAT 930 Reflection

• Good clients overall this semester